When the burner "does" lite, is it a nice blue flame of normal size? We recently experience much the same symptoms as you describe, but the flame was small and not real solid blue. Removed the regulator and dark brown oil poured out of it. Replaced it and now flame is quick and perfect.
Ron
Ron & Sandie
2013 Tiffin Phaeton 42LH Cummins ISL 400hp
Toad: 2011 GMC Terrain SLT2
Tow Bar: Sterling AT
Toad Brakes: Unified by U.S. Gear
TPMS: Pressure Pro
Member of: GS, FMCA, Allegro
RETIRED!! How sweet it is....